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Investments - Additional Information (Detail)
In Millions, unless otherwise specified
 12 Months Ended 1 Months Ended 12 Months Ended 12 Months Ended 1 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended
Dec. 31, 2012
USD ($)
Subsidiary
Kmt
Dec. 31, 2011
USD ($)
Dec. 31, 2010
USD ($)
Oct. 31, 2011
Ma'aden Joint Venture [Member]
Dec. 31, 2012
Ma'aden Joint Venture [Member]
Dec. 31, 2011
Ma'aden Joint Venture [Member]
USD ($)
Dec. 31, 2010
Ma'aden Joint Venture [Member]
USD ($)
Dec. 31, 2012
Alcoa [Member]
USD ($)
Y
Dec. 31, 2012
Alcoa [Member]
SAR
Y
Dec. 31, 2011
Alcoa [Member]
USD ($)
Dec. 31, 2012
Alcoa [Member]
Alcoa World Alumina and Chemicals [Member]
Dec. 31, 2012
Smelting and Rolling Mill Companies [Member]
USD ($)
Dec. 31, 2010
Smelting and Rolling Mill Companies [Member]
USD ($)
Dec. 31, 2012
Other Noncurrent Liabilities and Deferred Credits [Member]
USD ($)
Dec. 31, 2011
Other Noncurrent Liabilities and Deferred Credits [Member]
USD ($)
Oct. 31, 2011
Refining and Mining Company [Member]
USD ($)
Dec. 31, 2012
Refining and Mining Company [Member]
USD ($)
Dec. 31, 2011
Refining and Mining Company [Member]
USD ($)
Dec. 31, 2012
Fixed Income Securities [Member]
USD ($)
Dec. 31, 2011
Equity Securities [Member]
USD ($)
Dec. 31, 2012
Alumina Limited [Member]
Alcoa World Alumina and Chemicals [Member]
Dec. 31, 2011
Saudi Arabia Joint Venture [Member]
Scenario One [Member]
USD ($)
Dec. 31, 2011
Saudi Arabia Joint Venture [Member]
Scenario Two [Member]
USD ($)
Dec. 31, 2012
Becancour Smelter [Member]
Dec. 31, 2012
Boke Investment Company [Member]
Dec. 31, 2012
Compagnie Des Bauxites De Guinee [Member]
Dec. 31, 2012
Bauxite mining [Member]
Kmt
Dec. 31, 2012
Bauxite mining [Member]
Halco Mining, Inc. [Member]
Dec. 31, 2012
Bauxite mining [Member]
Minerao Rio Do Norte S.A. [Member]
Dec. 31, 2012
Alumina Refinery [Member]
Kmt
Dec. 31, 2012
Primary aluminum smelter [Member]
Kmt
Dec. 31, 2012
Rolling mill [Member]
Kmt
Dec. 31, 2012
Smelter Operation [Member]
Pechiney Reynolds Quebec, Inc. [Member]
Dec. 31, 2012
Smelter Operation [Member]
Becancour smelter in Quebec, Canada [Member]
Dec. 31, 2012
Smelter Operation [Member]
Alcoa [Member]
Schedule of Equity Method Investments [Line Items]                                                                      
Percent of equity investments in other entity 50.00%                   60.00%                   40.00%     49.90% 100.00% 51.00%   45.00% 18.20%       50.00% 50.10% 25.05%
Number of wholly-owned subsidiaries 2                                                                    
Dividends from equity investments $ 101 $ 100 $ 33                                                                
Joint venture shareholders agreement period, years         30 years                                                            
Joint venture shareholders agreement, automatic extension additional period, years         20 years                                                            
Projected capacity amount of processed bauxite, in kmt                                                     4,000     1,800 740 380      
Expanded capacity amount of processed bauxite, in Kmt 100                                                                    
Ownership interest in joint venture       74.90% 74.90%   74.90% 25.10% 25.10%       25.10%     25.10%                                      
Initial investment               80                                                      
Payment for pro rata share of pre-incorporation costs           22 34                                                        
Ownership interest in joint venture at fair market value         14.90%                                                            
Outstanding receivable for labor and other employee-related expenses 28 25                                                                  
Capital investment 1,860 1,626           10,800 40,500                                                    
Amount invested by Alcoa and Aluminum Financing Limited               1,100                                                      
Term of investment by Alcoa and Aluminum Financing Limited, years               5 5                                                    
Capital investment commitment paid-to-date 253 249           661                                                      
Equity investments 1,782 1,524           816   565                                                  
Project financing                       480 4,035     1,992                                      
Portion of project financing representing Alcoa interest in venture                       120 1,013     500                                      
Debt service requirements, principal                       121       60                                      
Debt service requirements, interest maximum                       60       25                                      
Fair value of guarantee included in other noncurrent liabilities and deferred credits 494                         10 8                                        
Combined fair value of guarantees                                 4 4                                  
Potential forfeiture of letter of credit                                           350 60                        
Other investments $ 78 $ 102                                 $ 67 $ 92